Since the invention of power vehicles, many different powertrain systems have been attempted, including a steam engine with a boiler or an electric motor with a storage battery. It was, however, the discovery of petroleum in 1856 and the fourstroke internal combustion engine invented by Otto in 1876, that provided the impetus for the modern motor vehicle industry.
Although fossil fuel emerged as the fuel of choice for motor vehicles, recent concerns regarding fuel availability and increasingly stringent federal and state emission regulations have renewed interest in alternative fuel powered vehicles. For example, alternative fuel vehicles may be powered by methanol, ethanol, natural gas, electricity, or a combination of these fuels.
A dedicated electric powered vehicle offers several advantages: electricity is readily available, an electric power distribution system is already in place, and an electric powered vehicle produces virtually no emissions. There are, however, several technological disadvantages that must be overcome before electric powered vehicles gain acceptance in the marketplace. For instance, the range of an electric powered vehicle is limited to approximately 100 miles, compared to approximately 300 miles for a similar fossil fuel powered vehicle. Further, the costs of batteries are significantly more than that of a comparable fossil fuel powered vehicle.
Hybrid powered vehicles, powered by both an internal combustion engine and an electric motor, have been widely proposed for overcoming the technical disadvantages of a dedicated electric vehicle while still offering an increased efficiency. The performance and range characteristics of a hybrid powered vehicle is comparable to a conventional fossil fuel powered vehicle. However, a great deal of development is still necessary in order to provide a hybrid electric vehicle which would be widely accepted by the consuming public.
The present invention deals with the issue of determining a desirable amount of braking torque distribution by an electric motor/generator and a friction brake system of a hybrid electric vehicle in order to provide efficient regeneration of braking energy into stored energy.
Accordingly, it is an object of the present invention to provide an improved brake blending strategy for a hybrid powertrain system.
To achieve the foregoing object, the present invention provides a hybrid electric powertrain system for a vehicle, including a transmission for driving a pair of wheels of the vehicle. A heat engine and an electric motor/generator are coupled to the transmission. A friction brake system is provided for applying a braking torque to the vehicle. A controller unit is provided for generating control signals to the electric motor/generator and the friction brake system for controllably braking the vehicle in response to a driver's brake command. The controller unit determines an amount of regenerative torque available and compares this value to a determined amount of brake torque requested for determining the control signals to the electric motor/generator and the friction brake system.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.